By: Lead Forecaster Daniel Crawley
We continue a multi-part series looking back at Hurricane Helene, its evolution and how it turned into the largest natural disaster in the history of Western North Carolina replacing major weather events such as the floods of 1916 and 1940.
Between now and Saturday (Sept 27), the official 1-year anniversary, we will look back at the storm from a forecaster’s perspective here at Foothills Weather Network. We will go over the factors that created a three-day rain event that brought historic flooding to many river basins in WNC along with the impact of strong winds as Helene itself moved in. We will also re-live the post-storm impacts that Helene brought to the region, including several of the counties that we cover daily at Foothills Weather Network.
Part 3 of the series focuses on the events of September 24th, 2024 and how everything was coming together from a meteorological standpoint for a high impact event to hit the Western Carolinas.
On the day prior, advisories began on what was Potential Tropical Cyclone Nine in the Western Caribbean Sea. However, as we got to the midday hours of Tuesday, the storm was quickly organizing and was upgraded to Tropical Storm Helene with the 11 am advisory from the National Hurricane Center.
The official NHC forecast at 11 am had Helene becoming a hurricane within the following 24 hours and a major hurricane as it approached the Florida Panhandle and Big Bend Region. The forecast track also had an accelerating storm at landfall; that caught our eye here in the inland southeast knowing the synoptic setup in place. The NHC forecast just help build confidence that rain and wind could impact the Western Carolinas.
One of the more notable aspects on this way was the already large size and scope of the storm in its formative stages just south of the Yucatan Channel.
Here locally on Sept 24, 2024, a stalled frontal boundary and developing upper low back over the Ozarks Region was producing scattered showers and thunderstorms. This was well ahead of any hurricane approach and even prior to the Predecessor Rain Event (PRE) that hit on the next day. Slowly but surely the ground was already becoming saturated in spotty areas.
Also, hurricane guidance was noted to have an eastward shift as Helene was named and now it showed a Big Bend Region landfall as compared to the previous couple days, a Panama City-Destin landfall.
The one thing Sept 24, 2024 did was increase our confidence enough to where our weather team began to use wording of “significant flood/wind damage possible” in a blog that was updated late the afternoon of 9/24. The FWN weather team also began frequent consulting with our emergency management partners at that point to share our concerns on how impactful it was going to be. For everyone in the room forecasting, the immediate flashback was to 2004 and the remnants of Hurricane Frances. We were thinking at that level once we got to within three days from the event.
European Model ensembles had widespread high probabilities of at least 4 inches of rain 72 hours before the event, plus a focused high probability of 8+ inches along the Eastern Continental Divide, which runs through the western sections of our coverage area. On top of that, the Weather Prediction Center issued it’s first “moderate risk” of flooding for the Western Carolinas.
It was becoming apparent by the time we all went to bed on Sept 24 that the Southern Appalachians was destined for some serious.
Coming Up: In Part 4, we go into detail about the beginning of the PRE rain event and increased wording behind our messaging along with everyone else in the weather enterprise. We also look into how the local community began to prepare for what was now looking like a potentially historic event. That chapter of the story will be made available on our website starting Thursday.